I like how you're adding little details here and there to really define Shepard's personality and thoughts. My only critique would be that it's seeming more like a retelling of Mass Effect 2 without any real original story, such as Shepard's background story or an AU. Perhaps you're building up to more of an original take in later chapters, which is fine. Other than that, I'm enjoying this. I look forward to how you write out Garrus and Shepard's relationship. That's always the fun part, right?